Microencapsulation improves inhibitory effects of transplanted olfactory ensheathing cells on pain after sciatic nerve injury

Advances of Schwann cells in peripheral nerve regeneration: From mechanism to cell therapy

Peripheral nerve injuries (PNIs) frequently occur due to various factors, including mechanical trauma such as accidents or tool-related incidents, as well as complications arising from diseases like tumor resection. These injuries frequently result in persistent numbness, impaired motor and sensory functions, neuropathic pain, or even paralysis, which can impose a significant financial burden on patients due to outcomes that often fall short of expectations. The most frequently employed clinical treatment for PNIs involves either direct sutures of the severed ends or bridging the proximal and distal stumps using autologous nerve grafts. However, autologous nerve transplantation may result in sensory and motor functional loss at the donor site, as well as neuroma formation and scarring. Transplantation of Schwann cells/Schwann cell-like cells has emerged as a promising cellular therapy to reconstruct the microenvironment and facilitate peripheral nerve regeneration. In this review, we summarize the role of Schwann cells and recent advances in Schwann cell therapy in peripheral nerve regeneration. We summarize current techniques used in cell therapy, including cell injection, 3D-printed scaffolds for cell delivery, cell encapsulation techniques, as well as the cell types employed in experiments, experimental models, and research findings. At the end of the paper, we summarize the challenges and advantages of various cells (including ESCs, iPSCs, and BMSCs) in clinical cell therapy. Our goal is to provide the theoretical and experimental basis for future treatments targeting peripheral nerves, highlighting the potential of cell therapy and tissue engineering as invaluable resources for promoting nerve regeneration.

Application and challenges of olfactory ensheathing cells in clinical trials of spinal cord injury

Spinal cord injury (SCI) can lead to severe motor, sensory and autonomic nervous dysfunction, cause serious psychosomatic injury to patients. There is no effective treatment for SCI at present. In recent years, exciting evidence has been obtained in the application of cell-based therapy in basic research. These studies have revealed the fact that cells transplanted into the host can exert the pharmacological properties of treating and repairing SCI. Olfactory ensheathing cells (OECs) are a kind of special glial cells. The application value of OECs in the study of SCI lies in their unique biological characteristics, that is, they can survive and renew for life, give full play to neuroprotection, immune regulation, promoting axonal regeneration and myelination formation. The function of producing secretory group and improving microenvironment. This provides an irreplaceable treatment strategy for the repair of SCI. At present, some researchers have explored the possibility of treatment of OECs in clinical trials of SCI. Although OECs transplantation shows excellent safety and effectiveness in animal models, there is still lack of sufficient evidence to prove the effectiveness of their clinical application in clinical trials. There has been an obvious stagnation in the transformation of OECs transplantation into routine clinical practice, and clinical trials of cell therapy in this field are still facing major challenges and many problems that need to be solved. Therefore, this paper summarized and analyzed the clinical trials of OECs transplantation in the treatment of SCI, and discussed the problems and challenges of OECs transplantation in clinical trials.

Chitosan biomaterial enhances the effect of OECs on the inhibition of sciatic nerve injury-induced neuropathic pain

Neuropathic pain is a common symptom experienced by most clinical diseases at different levels, and its treatment has always been a clinical difficulty. Therefore, it is particularly important to explore new and effective treatment methods. The role of olfactory ensheathing cells (OECs) in nerve injury and pain is recognized by different studies. Our previous study found that transplantation of OECs alleviated hyperalgesia in rats. However, single-cell transplantation lacks medium adhesion and support, and exerts limited analgesic effect. Therefore, on the basis of the previous study, this study investigated the effect of pain relief by co-transplanting OECs with chitosan (CS) (a biological tissue engineering material, as OECs were transplanted into the host medium) to the injured sciatic nerve. The results showed that the pain threshold of sciatic nerve injury of rats was significantly reduced, and the expression level of P2×4 receptor in the spinal cord was significantly increased. While olfactory ensheathing cells combined with chitosan (OECs+CS) transplantation could significantly relieve pain, and the analgesic effect was stronger than that of OECs transplantation alone. OECs+CS transplantation promoted the formation of sciatic nerve remyelination, improved the changes of demyelination, and promoted the repair of sciatic nerve injury more significantly. In addition, the effect of OECs+CS to down-regulate the expression of P2×4 receptor was significantly stronger than that of OECs transplantation, and exerted a better analgesic effect. These data reveal that OECs+CS have a better analgesic effect in relieving neuropathic pain induced by sciatic nerve injury, and provide a new therapeutic strategy for pain treatment.

Potential role of Schwann cells in neuropathic pain

Neuropathic pain (NPP) is a common syndrome associated with most forms of disease, which poses a serious threat to human health. NPP may persist even after the nociceptive stimulation is eliminated, and treatment is extremely challenging in such cases. Schwann cells (SCs) form the myelin sheaths around neuronal axons and play a crucial role in neural information transmission. SCs can secrete trophic factors to nourish and protect axons, and can further secrete pain-related factors to induce pain. SCs may be activated by peripheral nerve injury, triggering the transformation of myelinated and non-myelinated SCs into cell phenotypes that specifically promote repair. These differentiated SCs provide necessary signals and spatial clues for survival, axonal regeneration, and nerve regeneration of damaged neurons. They can further change the microenvironment around the regions of nerve injury, and relieve the pain by repairing the injured nerve. Herein, we provide a comprehensive overview of the biological characteristics of SCs, discuss the relationship between SCs and nerve injury, and explore the potential mechanism of SCs and the occurrence of NPP. Moreover, we summarize the feasible strategies of SCs in the treatment of NPP, and attempt to elucidate the deficiencies and defects of SCs in the treatment of NPP.

Olfactory ensheathing cells and neuropathic pain

Damage to the nervous system can lead to functional impairment, including sensory and motor functions. Importantly, neuropathic pain (NPP) can be induced after nerve injury, which seriously affects the quality of life of patients. Therefore, the repair of nerve damage and the treatment of pain are particularly important. However, the current treatment of NPP is very weak, which promotes researchers to find new methods and directions for treatment. Recently, cell transplantation technology has received great attention and has become a hot spot for the treatment of nerve injury and pain. Olfactory ensheathing cells (OECs) are a kind of glial cells with the characteristics of lifelong survival in the nervous system and continuous division and renewal. They also secrete a variety of neurotrophic factors, bridge the fibers at both ends of the injured nerve, change the local injury microenvironment, and promote axon regeneration and other biological functions. Different studies have revealed that the transplantation of OECs can repair damaged nerves and exert analgesic effect. Some progress has been made in the effect of OECs transplantation in inhibiting NPP. Therefore, in this paper, we provided a comprehensive overview of the biology of OECs, described the possible pathogenesis of NPP. Moreover, we discussed on the therapeutic effect of OECs transplantation on central nervous system injury and NPP, and prospected some possible problems of OECs transplantation as pain treatment. To provide some valuable information for the treatment of pain by OECs transplantation in the future.

Cell therapy for neuropathic pain

Neuropathic pain (NP) is caused by a lesion or a condition that affects the somatosensory system. Pathophysiologically, NP can be ascribed to peripheral and central sensitization, implicating a wide range of molecular pathways. Current pharmacological and non-pharmacological approaches are not very efficacious, with over half of NP patients failing to attain adequate pain relief. So far, pharmacological and surgical treatments have focused primarily on symptomatic relief by modulating pain transduction and transmission, without treating the underlying pathophysiology. Currently, researchers are trying to use cell therapy as a therapeutic alternative for the treatment of NP. In fact, mounting pre-clinical and clinical studies showed that the cell transplantation-based therapy for NP yielded some encouraging results. In this review, we summarized the use of cell grafts for the treatment of NP caused by nerve injury, synthesized the latest advances and adverse effects, discussed the possible mechanisms to inform pain physicians and neurologists who are endeavoring to develop cell transplant-based therapies for NP and put them into clinical practice.

Association between P2X3 receptors and neuropathic pain: As a potential therapeutic target for therapy

Neuropathic pain is a common clinical symptom of various diseases, and it seriously affects the physical and mental health of patients. Owing to the complex pathological mechanism of neuropathic pain, clinical treatment of pain is challenging. Therefore, there is growing interest among researchers to explore potential therapeutic strategies for neuropathic pain. A large number of studies have shown that development of neuropathic pain is related to nerve conduction and related signaling molecules. P2X3 receptors (P2X3R) are ATP-dependent ion channels that participate in the transmission of neural information and related signaling pathways, sensitize the central nervous system, and play a key role in the development of neuropathic pain. In this paper, we summarized the structure and biological characteristics of the P2X3R gene and discussed the role of P2X3R in the nervous system. Moreover, we outlined the related pathological mechanisms of pain and described the relationship between P2X3R and chronic pain to provide valuable information for development of novel treatment strategies for pain.

Designing Olfactory Ensheathing Cell Transplantation Therapies: Influence of Cell Microenvironment

Olfactory ensheathing cell (OEC) transplantation is emerging as a promising treatment option for injuries of the nervous system. OECs can be obtained relatively easily from nasal biopsies, and exhibit several properties such as secretion of trophic factors, and phagocytosis of debris that facilitate neural regeneration and repair. But a major limitation of OEC-based cell therapies is the poor survival of transplanted cells which subsequently limit their therapeutic efficacy. There is an unmet need for approaches that enable the in vitro production of OECs in a state that will optimize their survival and integration after transplantation into the hostile injury site. Here, we present an overview of the strategies to modulate OECs focusing on oxygen levels, stimulating migratory, phagocytic, and secretory properties, and on bioengineering a suitable environment in vitro.

Transplantation of microencapsulated neural stem cells inhibits neuropathic pain mediated by P2X7 receptor overexpression

BACKGROUND

Neuropathic pain (NPP) is a common clinical symptom, its pathological mechanism is complex, and there is currently no good treatment method. Therefore, exploring the treatment method of NPP is a critical issue that needs to be urgently solved.

METHODS

Neural stem cells (NSC) and microencapsulated neural stem cells (MC-NSC) were transplanted into the site of sciatic nerve injury, and behavioral methods were used to detect changes in pain. Expression levels of P2X7R were detected in the dorsal root ganglion (DRG) by molecular biological methods.

RESULTS

After sciatic nerve injury, mechanical withdrawal thresholds (MWT) and thermal withdrawal latency (TWL) of rats were significantly reduced, the expression levels of P2X7R in the DRG were significantly increased. After transplantation of NSC and MC-NSC, it was found that expression levels of P2X7R were significantly reduced and pain was significantly suppressed. Importantly, compared with NSC transplantation, MC-NSC could better reduce the expression levels of P2X7R and inhibit pain.

CONCLUSION

MC-NSC can better decrease the expression levels of P2X7R and relieve NPP. Our results provide a novel method and data support for the treatment of NPP.

Transplantation of microencapsulated olfactory ensheathing cells inhibits the P2X2 receptor over-expressionmediated neuropathic pain in the L4-5 spinal cord segment

OBJECTIVES

The purpose of this study was to determine the effect of microencapsulated olfactory ensheathing cells (MC-OECs) transplantation on neuropathic pain (NPP) caused by sciatic nerve injury in rats, and its relationship with the expression levels of P2X2 receptor (P2X2R) in the L4-5 spinal cord segment.

METHODS

Olfactory bulb tissue was removed from a healthy Sprague-Dawley (SD) rat for culturing olfactory ensheathing cells (OECs). Forty-eight SD rats were randomly divided into four groups (12 per group): the sham, chronic constriction injury (CCI), olfactory ensheathing cells (OECs), and MC-OECs groups. On days 7 and 14 after surgery, the mechanical withdrawal thresholds (MWT) were measured by using behavioral method. The expression levels of P2X2R in the L4-5 spinal cord segment were detected by in situ hybridization and Western blotting.

RESULTS

On days 7 and 14 post-surgical, the MWT of rats from high to low were the sham, MC-OECs, OECs, and CCI groups, the MWT of rats in the MC-OECs groups were higher than that in OECs groups. The expression levels of P2X2R in the L4-5 spinal cord segment from high to low were the CCI, OECs, MC-OECs, and sham groups, the expression levels of P2X2R were lower than that in OECs groups. All differences between groups were statistically significant (p value <.05).

CONCLUSIONS

OECs and MC-OECs transplantation can reduce the expression levels of P2X2R genes in the L4-5 spinal cord segment, and relieve NPP. The therapeutic efficacy of MC-OECs transplantation was better than the transplantation of OECs.

Microencapsulated olfactory ensheathing-cell transplantation reduces pain in rats by inhibiting P2X4 receptor overexpression in the dorsal root ganglion

The aim of this study was to determine the role of microencapsulated olfactory ensheathing-cell transplantation (MC-OEC) in rats in which pain was induced by sciatic nerve injury, and its relationship with the expression level of the P2X4 receptor in the dorsal root ganglion. Olfactory bulb tissues of healthy Sprague-Dawley rats were collected to culture olfactory ensheathing cells using differential attachment methods. Ninety-six healthy Sprague-Dawley rats were randomly assigned to the sham, chronic constriction injury (CCI), olfactory ensheathing cell (OEC), and MC-OEC groups. Mechanical paw withdrawal thresholds were measured 7 and 14 days after surgery. The expression of P2X4 receptor genes in the L4-5 dorsal root ganglion was detected by reverse transcriptase polymerase chain reaction, fluorescence in-situ hybridization, and western blotting. Seven and 14 days after the surgery, the mechanical paw withdrawal thresholds of rats in the MC-OEC, OEC, and CCI groups were decreased compared with the sham group. The expression level of the P2X4 receptor in the L4-5 dorsal root ganglion in CCI, OEC, and MC-OEC groups was increased compared with the sham group. All differences between groups were statistically significant. Transplantation of OEC and MC-OEC can reduce neuropathic pain and inhibit the overexpression of the P2X4 receptor in the L4-5 dorsal root ganglion. The transplantation of MC-OEC was more effective in the MC-OEC group than in the OEC group.

1,8-cineole decreases neuropathic pain probably via a mechanism mediating P2X3 receptor in the dorsal root ganglion

1,8-cineole is a natural monoterpene cyclic ether present in eucalyptus and has been reported to exhibit anti-inflammatory and antioxidant effects. The therapeutic effects of 1,8-cineole on neuropathic pain and the molecular mechanisms of its pharmacological actions remain largely unknown. In the present study, we investigated the analgesic mechanisms of orally administered 1,8-cineole in a rat model of chronic constriction injury (CCI) and examined the drug-induced modulation of P2X3 receptor expression in dorsal root ganglia. The mechanical withdrawal threshold and thermal withdrawal latency were measured in rats to assess behavioural changes 7 and 14 days after CCI surgery. Changes in P2X3 receptor mRNA expression of L4-5 dorsal root ganglia were analysed using quantitative real-time polymerase chain reaction at the 7th and 14th postoperative day. Additionally, we examined the expression of P2X3 receptor protein in L4-5 dorsal root ganglia 7 and 14 days after surgery using immunohistochemistry and western blots. We found that 1,8-cineole can alleviate pathological pain caused by P2X3 receptor stimulation and explored new methods for the prevention and treatment of neuropathic pain.

Microencapsulated Schwann cell transplantation inhibits P2X2/3 receptors overexpression in a sciatic nerve injury rat model with neuropathic pain

Transplantation of Schwann cells (SCs) can promote axonal regeneration and formation of the myelin sheath, reduce inflammation, and promote repair to the damaged nerve. Our previous studies have shown that transplantation of free or micro-encapsulated olfactory ensheathing cells can relieve neuropathic pain. There are no related reports regarding whether the transplantation of micro-encapsulated SCs can alleviate neuropathic pain mediated by P2X2/3 receptors. In the present study, we micro-encapsulated SCs in alginic acid and transplanted them into the region surrounding the injured sciatic nerve in the rat model of chronic constriction injury (CCI). The mechanical withdrawal threshold and thermal withdrawal latency were measured to assess changes in behavior 14 days after the surgery in CCI model rats. Ultrastructural changes in the injured sciatic nerve were assessed using transmission electron microscopy. Co-expression of P2X2/3 receptors with other markers in neurons in the L_4-5 dorsal root ganglia (DRG) were assessed using double-label immunofluorescence 14 days after surgery. We determined P2X2/3 mRNA expression and protein level changes in the DRG using quantitative real-time polymerase change reaction technology and Western blotting analysis. We have investigated that the transplantation of micro-encapsulated SCs can alleviate pathological pain caused by P2X2/3 receptor stimulation and explored new methods for the prevention and treatment of neuropathic pain.

Microencapsulated Schwann cell transplantation inhibits P2X3 receptor expression in dorsal root ganglia and neuropathic pain

Schwann cell transplantation is a promising method to promote neural repair, and can be used for peripheral nerve protection and myelination. Microcapsule technology largely mitigates immune rejection of transplanted cells. We previously showed that microencapsulated olfactory ensheathing cells can reduce neuropathic pain and we hypothesized that microencapsulated Schwann cells can also inhibit neuropathic pain. Rat Schwann cells were cultured by subculture and then microencapsulated and were tested using a rat chronic constriction injury (CCI) neuropathic pain model. CCI rats were treated with Schwann cells or microencapsulated Schwann cells and were compared with sham and CCI groups. Mechanical withdrawal threshold and thermal withdrawal latency were assessed preoperatively and at 1, 3, 5, 7, 9, 11 and 14 days postoperatively. The expression of P2X3 receptors in L4-5 dorsal root ganglia of the different groups was detected by double-label immunofluorescence on day 14 after surgery. Compared with the chronic constriction injury group, mechanical withdrawal threshold and thermal withdrawal latency were higher, but the expression of P2X3 receptors was remarkably decreased in rats treated with Schwann cells and microencapsulated Schwann cells, especially in the rats transplanted with microencapsulated Schwann cells. The above data show that microencapsulated Schwann cell transplantation inhibits P2X3 receptor expression in L4-5 dorsal root ganglia and neuropathic pain.

Olfactory ensheathing glia cell therapy and tubular conduit enhance nerve regeneration after mouse sciatic nerve transection

The regenerative potential of the peripheral nervous system (PNS) is widely known, but functional recovery, particularly in humans, is seldom complete. Therefore, it is necessary to resort to strategies that induce or potentiate the PNS regeneration. Our main objective was to test the effectiveness of Olfactory Ensheathing Cells (OEC) transplantation into a biodegradable conduit as a therapeutic strategy to improve the repair outcome after nerve injury. Sciatic nerve transection was performed in C57BL/6 mice; proximal and distal stumps of the nerve were sutured into the collagen conduit. Two groups were analyzed: DMEM (acellular grafts) and OEC (1×105/2μL). Locomotor function was assessed weekly by Sciatic Function Index (SFI) and Global Mobility Test (GMT). After eight weeks the sciatic nerve was dissected for morphological analysis. Our results showed that the OEC group exhibited many clusters of regenerated nerve fibers, a higher number of myelinated fibers and myelin area compared to DMEM group. The G-ratio analysis of the OEC group showed significantly more fibers on the most suitable sciatic nerve G-ratio index. Motor recovery was accelerated in the OEC group. These data provide evidence that the OEC therapy can improve sciatic nerve functional and morphological recovery and can be potentially translated to the clinical setting.